The proposed research will attempt to: 1) Define the physical and/or structural changes which occur in elementary bodies following phagocytosis by susceptible and nonsusceptible cells; 2) Define the biochemical events associated with the early phase of the growth cycle; 3) Determine the time course and nature of the chlamydial mRNA and protein molecules synthesized throughout the growth cycle; 4) Accurately define the temporal sequence of chlamydial DNA replication in the infected cell; 5) Analyze replicative forms of chlamydial DNA; 6) Isolate membrane-DNA complex to analyze the replication of chlamydial DNA and to obtain replicative DNA polymerases. We plan to use a variety of methods including electron microscopy, density gradient centrifugation, and molecular hybridization.